Electronic packages having leads arranged in a ball grid array (BGA) or a land grid array (LGA) are known. These packages have a relatively low height which is desirable for saving space in electronic assemblies. The packages may be surface mounted directly on a circuit board in a soldering process wherein the leads become solder bonded to a corresponding array of circuit pads on the board. However, solder bonding has the drawback that the package is not easily removable for replacement or upgrade. It is often desirable to provide a connector for mounting the electronic package on the circuit board in a separable fashion. Keeping the connector height low is a major consideration.
Connectors are known for removably mounting a BGA or LGA package on a circuit board. Such connectors are disclosed in U.S. Pat. Nos. 4,511,197; 4,513,353; 4,647,124; and 4,699,593. These connectors comprise a substantially flat dielectric housing which resides between the electronic package and the circuit board. The housing has an array of cavities in which are disposed electrical contacts arranged in correspondence with the array of leads of the electronic package. Each of the contacts has a pair of oppositely extending noses which project beyond external surfaces of the connector housing. When the package is mounted on the connector, each of the contacts has one nose engaged with a respective lead of the package and the other nose engaged with a respective pad on the board. A compressive force is applied to the package and the board to assure firm engagement of each nose with its respective lead or pad. Typically, the compressive force may be applied by pressure plates which are fastened together to sandwich the package, connector and board therebetween.
Considering the circuit board to lie in a horizontal plane, the contacts must be compliant in the vertical direction in order to assure engagement with all of the leads and pads despite any coplanarity mismatch between the package and the board. Further, the contacts, which exert a spring force when compressed, should have a low spring rate to keep normal forces on the leads and pads within a desired range. High compliancy and a low spring rate can be accomplished by contacts which have a long spring length and a small cross-sectional area, but increases in spring length are associated with increases in inductance, and reductions in cross-sectional area are accompanied by increases in electrical resistance, both of which are detrimental to electrical performance.
Accordingly, it is an object of the present invention to provide a contact for an electrical connector which offers high compliancy and a low spring rate along with low electrical resistance and a reduction in self-inductance effects.